Fluid driven hammers as well as other working devices are commonly attached to the end of a boom for manipulation and use. Hammers are commonly used in the construction industry for the demolition of concrete, fracturing of rock, driving posts, etc. In general, a hammer 10 includes a housing or casing 12 which defines a hollow interior (FIG. 12). The interior is subdivided by an annular shoulder 20 into a rear tubular cavity 16 and a forward tubular cavity 18. Annular shoulder 20 defines a central orifice 22 interconnecting the two cavities. A piston 26 and tool 24 are movably supported in cavities 16, 18, respectively. The fluid connections have been omitted for clarity, as these are well known in the industry.
Tool 24 is typically a rigid, rod-like member which is intended to engage the ground, post, etc., and perform the desired work. For purposes of illustration only, a working tool for breaking up concrete and the like will be described. Nevertheless, a wide variety of other types of tools could be used in connection with the hammer. The illustrated tool 24 is comprised of a generally cylindrical body 28, an enlarged head 30, and a pointed free end 32. The head end 30 and the upper portion of body 28 are reciprocally received within cavity 18. Body 28 extends outwardly through opening 34 defined in the forward end of casing 12, so that working end 32 is exposed for engaging the bearing surface, such as concrete C. Orifice 22 and opening 34 each define a smaller width than that defined by head 30, to thereby confine head 30 within cavity 18. Alternatively, a pin is used to confine the tool instead of enlargement 30.
Piston 26 is comprised of a generally cylindrical body segment 36 and an impact segment 38. Body segment 36 is matingly received within rear cavity 16 of casing 12 for reciprocal movement therewithin. Impact segment 38 as illustrated protrudes forwardly from body 36 with a reduced diameter. Nevertheless, the piston is frequently constructed as a uniform cylindrical member throughout its length. In any event, impact segment 38 is received through orifice 22 during the forward end of each stroke. In use, piston 26 is rapidly reciprocated within cavity 16 to repeatedly strike working tool 24. Specifically, impact segment 38 is driven through orifice 22 to repeatedly strike head 30, which in turn imparts an impact force to the bearing surface (such as concrete C) by pointed end 32. The movement of piston 26 is caused by selectively feeding pressurized hydraulic fluid or air into cavity 16 on opposing sides of piston 26. The control of the fluid is effected by a pump and a plurality of valves (not shown).
Preferably, head 30 of tool 24 is abutted against shoulder 20 when struck by piston 26, to maximize the force of each blow. The downward force applied by the boom to which the hammer is attached is intended to present the tool in this position for each impact. However, due to the limitations of manipulating a boom and the construction of prior art mounting brackets, the optimum operation is often not realized.
In a typical operation of a fluid driven hammer prior to the present invention, tool 24 begins the operation with head 30 engaged against shoulder 20 (FIGS. 12 and 13A). In this position, tool 24 receives the maximum impact force from the reciprocated piston 26. During operation, the casing 12 is intended to follow tool 24 after each blow so that head 30 is in contact with shoulder 20. However, in practice, the downward pressure applied by the boom to casing 12 is not sufficient to overcome the friction between casing 12 and tool 24 to allow shoulder 20 to rest against the tool. Hence, a gap is produced between shoulder 20 and head 30 (FIGS. 13B and 14). This situation often becomes aggravated so that the head gradually progresses farther and farther away from shoulder 20 before each successive impact of piston 26. As can be appreciated, this causes the piston to impact the working tool 24 at successively lower positions in its downstroke. As piston 26 travels downwardly past the optimal striking point (i.e., where head 30 abuts shoulder 20), it begins to slow down. As a result, less force is imparted to tool 24 each time head 30 fails to return to shoulder 20. In fact, the farther head 30 is separated from shoulder 20, the less force it receives from piston 26. In certain instances, the problem can become so acute that piston 26 does not even strike tool 24 (FIG. 13C).
This shortcoming is primarily the result of the tool experiencing excessive friction. The magnitude of the friction is a function of the bearing material, lubricants, and side loads generated during operation. Side loads are caused when tool 24 and casing 12 are not in axial alignment with each other (FIG. 14). The magnitude of the side loads varies depending upon the nature and characteristics of the bearing material and the direction of the force applied to the hammer by the boom. In the prior art, the force applied to the hammer has tended to create, rather than avoid, the generation of such side forces.
In the construction industry, a number of different carriers are provided with articulated booms. For illustration purposes only, the boom of a backhoe will be discussed; although other types of booms and carriers could be used. A typical backhoe boom 40 includes a pair of arms 42, 44 (FIG. 15). First arm 42 is pivotally attached at its proximate end 42 to carrier 48, and its remote end to second arm 44. Second arm 44 (commonly referred to as the "stick") projects outwardly from first arm 42 and supports hammer 10 on its free end 52. The movement of articulated boom 40 is effected by a series of hydraulic cylinders 54A-C. More specifically, the first hydraulic cylinder 54A is attached between carrier 48 and first arm 42 for controlling the vertical pivotal movement of first arm 42 indicated by arrow 56. Cylinder 54B is connected between first arm 42 and second arm 44 for pivoting second arm 44 in a vertical direction as indicated by arrow 58. Hammer 10 is then pivotally swingable via the operation of hydraulic cylinder 54C working in combination with the box end linkage 60. The pivotal sweeping motion of hammer 10 is generally indicated by arrows 62.
Mounting brackets 65 are typically used to attach the hammer or other working device to the boom. One known mounting bracket is shown in FIG. 11. In this construction, bracket 65 includes a base plate 67, a pair of mounting flanges 69, and a pair of mounting ears 71. Mounting flanges 69 extend outward from base plate 67 and are spaced apart to receive therebetween the end of the stick 44 and a brace 73 of box end linkage 60. Each flange 69 further defines a pair of spaced apart bores (not shown) which are aligned with corresponding bores (not shown) in the stick and brace, respectively. Pins 79 are received through the aligned bores to couple bracket 65 to boom 40. Mounting ears 71 extend from the side of base plate 67 opposite mounting flanges 69. Ears 71, like flanges 69, are spaced apart and each define a pair of spaced apart bores (not shown). Ears 71 receive therebetween a pair of side plates 85 welded or otherwise secured to the sides of casing 12 of hammer 10. Each side plate also defines a pair of bores (not shown) which are aligned with the bores of ears 71. Pins 87 are received through the aligned bores of side plates 85 and ears 71 to couple hammer 10 to bracket 65.
Cylinder 54C is operable to swing hammer 10 about pin 79 received through flange 69 and stick 44. This causes the hammer to be moved in a sweeping motion such that the pointed end 32 of tool 24 is moved along an arc. In fact, with this construction, the working end 32 is moved the greatest distance of any of the components with each adjustment of cylinder 54C. As a result, a small adjustment of the cylinder can result in a large displacement of the working end 32. As can be appreciated, operation of the other cylinders 54A, 54B also causes the hammer to be swept in an arc about a pin positioned more rearward along the boom. This type of adjustment makes accurate placement of the working end a difficult task.
As discussed above, it is intended that tool 24 be positioned at its fully retracted position (i.e., with head 30 engaged against shoulder 20) to receive each successive piston blow (FIGS. 12 and 13A). This positioning of tool 24 is accomplished by the downward force which is applied by boom 40. However, in view of the multiple articulation of the boom, a direct forward axially applied pressure to hammer 10 is virtually impossible to attain, even for an experienced operator. As best seen in FIGS. 14 and 15, expansion of hydraulic cylinder 54C functions to arcuately swing working end 32 rather than apply a downward force thereto. While this arcuate swinging could theoretically be compensated for by cylinders 54A, 54B, it as a practical matter is not generally successfully achieved. Therefore, as tool 24 becomes embedded in bearing material C, the force applied by cylinder 54C tends to increasingly bind casing 12 against tool 24 (FIG. 14). This operation thus creates the excessive side forces commonly experienced in the prior art.